JP2008121598A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To release captured SOx from SOx capture agent while preventing SOx from being stored in a NOx storage reduction catalyst. <P>SOLUTION: An exhaust emission control module 22 is provided with a SOx trap catalyst 24 and the NOx storage reduction catalysts 25, 26 mutually arranged in series, and is connected to an upstream side exhaust pipe 21 and a downstream side exhaust pipe 23 to position the SOx trap catalyst 24 in an upstream of the NOx storage reduction catalysts 25, 26. The exhaust emission control module 22 can be re-connected to the exhaust pipes 21, 23 by removing the exhaust emission control module 22 from the exhaust pipes 21, 23 and reversing the exhaust emission control module 22 to position the SOx trap catalyst 24 in the downstream of the NOx storage reduction catalysts 25, 26. If it is judged that SOx quantity captured by the SOx trap catalyst 24 exceeds an allowable upper limit, the exhaust emission control module 22 is reversed and is connected to the exhaust pipes 21, 23, and SOx is released from the SOx trap catalyst 24. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  When the air-fuel ratio of the inflowing exhaust gas is lean, NOx in the exhaust gas is occluded, and when the air-fuel ratio of the inflowing exhaust gas becomes rich, the NOx occlusion reduction catalyst that releases and reduces the stored NOx is provided in the engine exhaust passage. Internal combustion engines arranged inside are known. In this internal combustion engine, NOx generated when combustion is performed under a lean air-fuel ratio is stored in the NOx storage reduction catalyst. On the other hand, when the NOx storage capacity of the NOx storage catalyst approaches saturation, the air-fuel ratio of the exhaust gas is temporarily made rich, whereby NOx is released from the NOx storage catalyst and reduced.

  By the way, sulfur is contained in the fuel and the lubricating oil, and therefore SOx is contained in the exhaust gas. This SOx is stored in the NOx storage reduction catalyst together with NOx. However, this SOx is not released from the NOx occlusion catalyst simply by making the air-fuel ratio of the exhaust gas rich, so the amount of SOx occluded in the NOx occlusion reduction catalyst gradually increases. As a result, the amount of NOx that can be stored gradually decreases.

  Therefore, an internal combustion engine in which a SOx trap catalyst is disposed in an engine exhaust passage upstream of the NOx storage reduction catalyst in order to prevent SOx from being fed into the NOx storage reduction catalyst is known (see Patent Document 1). In this internal combustion engine, SOx contained in the exhaust gas is captured by the SOx trap catalyst, and therefore, the SOx is prevented from flowing into the NOx storage reduction catalyst. As a result, it is possible to prevent the NOx occlusion capability from being reduced by the SOx occlusion.

  However, when the SOx trapping capacity of the SOx trap catalyst reaches saturation, SOx discharged from the internal combustion engine may pass through the SOx trap catalyst and reach the NOx storage reduction catalyst, and may be stored in the NOx storage reduction catalyst. In this case, if SOx secured from the SOx trap catalyst is released, the SOx trapping capacity of the SOx trap catalyst is increased again, but the released SOx may be absorbed by the NOx storage reduction catalyst.

  Therefore, in the internal combustion engine of Patent Document 1, the capacity of the SOx trap catalyst is increased so that the SOx trap catalyst is not saturated until the vehicle is purchased and discarded. As a result, SOx discharged from the internal combustion engine does not pass through the SOx trap catalyst, and SOx captured from the SOx trap catalyst is not released. Therefore, there is no possibility that SOx is stored in the NOx storage reduction catalyst.

JP 2005-133610 A

  By the way, the SOx trap catalyst and the NOx occlusion reduction catalyst are generally arranged under the vehicle floor. However, a large space cannot always be secured under the vehicle floor, and there is a limit in increasing the capacity of the SOx trap catalyst. Further, when a large amount of sulfur is contained in the fuel or lubricating oil, the SOx trap catalyst may be saturated with SOx even if the capacity of the SOx trap catalyst is increased. Therefore, in practice, the SOx trapped from the SOx trap catalyst may have to be released. In this case, it is necessary to prevent the released SOx from being stored in the NOx storage reduction catalyst.

  In order to solve the above problems, according to the present invention, the SOx trapping agent that temporarily captures SOx contained in the exhaust gas and the NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean. And an exhaust gas purification module in which an NOx absorbent that releases absorbed NOx when the air-fuel ratio of the exhaust gas flowing into the exhaust gas becomes rich is arranged in series with each other, and the SOx trapping agent is an NOx absorbent. It is connected to the engine exhaust pipe so as to be located upstream, and the exhaust purification module is removed from the exhaust pipe so that the SOx trapping agent is inverted so that it is located downstream of the NOx absorbent so that it can be connected again to the exhaust pipe. Yes.

  The SOx captured from the SOx trap can be released while preventing SOx from being stored in the NOx storage and reduction catalyst.

  FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. However, the present invention can also be applied to a spark ignition type internal combustion engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the air flow meter 8. An electrically controlled throttle valve 10 is arranged in the intake duct 6, and a cooling device 11 for cooling intake air flowing in the intake duct 6 is arranged around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the exhaust aftertreatment device 20.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 12, and an electrically controlled EGR control valve 13 is disposed in the EGR passage 12. A cooling device 14 for cooling the EGR gas flowing in the EGR passage 12 is disposed around the EGR passage 12. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 14, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 16 through a fuel supply pipe 15. Fuel is supplied into the common rail 16 from an electronically controlled fuel pump 17 with variable discharge amount, and the fuel supplied into the common rail 16 is supplied to the fuel injection valve 3 through each fuel supply pipe 15.

  The exhaust aftertreatment device 20 includes an upstream exhaust pipe 21 connected to the outlet of the exhaust turbine 7b, an exhaust purification module 22 connected to the upstream exhaust pipe 21, and an exhaust pipe 23 connected to the exhaust purification module 22. It has. The exhaust purification module 22 includes, for example, an SOx trap 24 arranged in series in a single casing, a first NOx storage reduction catalyst 25, and a second NOx storage reduction catalyst 26. Further, oxidation catalysts 21c and 23c are arranged at the downstream end of the upstream exhaust pipe 21 and the upstream end of the downstream exhaust pipe 23, respectively. A differential pressure sensor 26 for detecting the differential pressure across the first NOx storage reduction catalyst 25 and a temperature sensor 27 for detecting the temperature of the first NOx storage reduction catalyst 25 are attached to the exhaust module 22. . One of the first NOx storage reduction catalyst 25 and the second NOx storage reduction catalyst 26 may be omitted.

  On the other hand, a fuel addition valve 28 is attached to the exhaust manifold 5 as shown in FIG. Fuel is added to the fuel addition valve 28 from the common rail 16, and fuel is added from the fuel addition valve 28 into the exhaust manifold 5. In an embodiment according to the invention, this fuel consists of light oil. The fuel addition valve 28 can also be attached to the upstream side exhaust pipe 21.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36. It comprises. The output signals of the air flow meter 8, the differential pressure sensor 26, and the temperature sensor 27 are input to the input port 35 via corresponding AD converters 37, respectively. A load sensor 40 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 39 is connected to the accelerator pedal 39, and the output voltage of the load sensor 40 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, a crank angle sensor 41 that generates an output pulse every time the crankshaft rotates by 15 °, for example, and an SOx release switch 42 described later are connected to the input port 35. The CPU 34 calculates the engine speed Ne based on the output pulse from the crank angle sensor 41. On the other hand, the output port 36 is connected to the fuel injection valve 3, the throttle valve 10 drive device, the EGR control valve 13, the fuel pump 17, the fuel addition valve 28, and the alarm device 43 through corresponding drive circuits 38. The alarm device 43 is constituted by a lamp, for example.

  In the embodiment according to the present invention, the exhaust purification module 22 is detachably connected to the exhaust pipes 21 and 23. That is, as shown in FIG. 1, the exhaust purification module 22 has flanges 22a and 22b at both ends, the flange 22a is provided at the downstream end of the upstream exhaust pipe 21, and the flange 22b is provided downstream. The side exhaust pipe 23 is connected to a flange 23u provided at the upstream end. Here, the flange 22 a can be connected to the flange 23 u of the downstream exhaust pipe 23, and the flange 22 b can be connected to the flange 21 d of the upstream exhaust pipe 21. Therefore, the exhaust purification module 22 is removed from the exhaust pipes 21 and 23, and the exhaust purification module 22 is inverted so that the SOx trapping agent 24 is located downstream of the NOx storage reduction catalysts 25 and 26 as shown in FIG. , 23 can be connected again. During normal operation, the exhaust module 22 is connected to the exhaust pipes 21 and 23 so that the SOx trap 24 is positioned upstream of the NOx storage and reduction catalysts 25 and 26 as shown in FIG.

  The first NOx storage reduction catalyst 25 is carried by, for example, a particulate filter 25a. 3A and 3B show the structure of the particulate filter 25a. 3A shows a front view of the particulate filter 25a, and FIG. 3B shows a side sectional view of the particulate filter 25a. As shown in FIGS. 3A and 3B, the particulate filter 25a has a honeycomb structure and includes a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust gas outflow passage 51 whose upstream end is closed by a plug 53. In addition, the hatched part in FIG. Therefore, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 are alternately arranged via the thin partition walls 54. In other words, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 are each surrounded by the four exhaust gas outflow passages 51, and each exhaust gas outflow passage 51 is surrounded by the four exhaust gas inflow passages 50. Arranged so that.

  The particulate filter 25 is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 50 is contained in the surrounding partition wall 54 as shown by an arrow in FIG. Through the exhaust gas outflow passage 51 adjacent thereto.

  In the embodiment according to the present invention, a catalyst carrier made of alumina, for example, is supported on the peripheral wall surfaces of the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51, that is, on both side surfaces of the partition walls 54 and on the pore inner wall surfaces of the partition walls 54. FIG. 4 schematically shows a cross section of the surface portion of the catalyst carrier 60. As shown in FIG. 4, a noble metal catalyst 61 made of platinum Pt, for example, is dispersed and supported on the surface of the catalyst carrier 60, and a layer of NOx absorbent 62 is further formed on the surface of the catalyst carrier 60. Has been.

  On the other hand, the second NOx occlusion reduction catalyst 26 is supported on a monolith catalyst 26a having a honeycomb structure as shown in FIG. 5. The monolith catalyst 26a is separated from each other by a thin partition wall 70, and the axis of the monolith catalyst 26 is obtained. A plurality of exhaust gas flow passages 71 extending straight in the direction are provided. As shown in FIG. 4, a catalyst carrier 60 is also supported on both side surfaces of each partition wall 70, and a noble metal catalyst 61 is dispersedly supported on the surface of the catalyst carrier, and a layer of NOx absorbent 62. Is formed.

  In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 61, and the components constituting the NOx absorbent 62 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, and calcium Ca. At least one selected from rare earths such as alkaline earth, lanthanum La, and yttrium Y is used.

  When the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NOx storage reduction catalysts 25 and 26 is referred to as the air-fuel ratio of the exhaust gas, the NOx absorbent 62 is exhaust gas. NOx is absorbed when the air-fuel ratio of the engine is lean, and NOx is absorbed and released when the oxygen concentration in the exhaust gas decreases.

That is, the case where barium Ba is used as a component constituting the NOx absorbent 62 will be described as an example. When the air-fuel ratio of the exhaust gas is lean, that is, when the oxygen concentration in the exhaust gas is high, the NO contained in the exhaust gas 4 is oxidized on the platinum Pt 61 to become NO ₂ as shown in FIG. 4, and then absorbed into the NOx absorbent 62 and combined with barium oxide BaO to form the nitrate ion NO ₃ ⁻ in the NOx absorbent 62. Spread. In this way, NOx is absorbed into the NOx absorbent 62. Exhaust oxygen concentration in the _gas, NO ₂ is produced on a high as long as the surface of the platinum PT61, unless NO ₂ to NOx absorbing capability of the NOx absorbent 62 is not saturated is absorbed in the NOx absorbent 62 nitrate ions NO ₃ ^- is Generated.

On the other hand, if the air-fuel ratio of the exhaust gas is made rich or stoichiometric, the oxidation concentration in the exhaust gas decreases, so that the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus NOx absorption The nitrate ions NO ₃ ⁻ in the agent 62 are released from the NOx absorbent 62 in the form of NO ₂ . Next, the released NOx is reduced by unburned HC and CO contained in the exhaust gas.

  In the internal combustion engine shown in FIG. 1, combustion is continued under a lean air-fuel ratio, and unless the fuel is added from the fuel addition valve 28, the air-fuel ratio of the exhaust gas flowing into the NOx absorbent 62 is kept lean. At this time, NOx in the exhaust gas is absorbed into the NOx absorbent 62. However, if the combustion under the lean air-fuel ratio is continuously performed, the NOx absorbent capacity of the NOx absorbent 62 is saturated during that time, and therefore the NOx absorbent 62 cannot absorb NOx. Therefore, in the embodiment according to the present invention, the air-fuel ratio of the exhaust gas is temporarily made rich by adding the fuel from the fuel addition valve 28 before the absorption capacity of the NOx absorbent 62 is saturated, and thereby the NOx absorbent 62 to the NOx. To be released.

Meanwhile, the exhaust gas contains SOx, that is, SO _2, the SO ₂ When this SO ₂ flows into the NOx storage-reduction catalyst 25 becomes oxidized SO ₃ in platinum PT61. Next, this SO ₃ is absorbed in the NOx absorbent 62 and combined with barium oxide BaO, while diffusing into the NOx absorbent 62 in the form of sulfate ions SO ₄ ²⁻ to produce stable sulfate BaSO ₄ . However, since the NOx absorbent 62 has a strong basicity, this sulfate BaSO ₄ is stable and difficult to decompose, and if the air-fuel ratio of the exhaust gas is simply made rich, the sulfate BaSO ₄ remains as it is without being decomposed. . Therefore, the sulfate BaSO ₄ increases in the NOx absorbent 62 as time elapses, and thus the amount of NOx that can be absorbed by the NOx absorbent 62 decreases as time elapses.

  When the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 25, 26 is made rich with the temperature of the NOx storage reduction catalyst 25, 26 raised to the SOx release temperature of 600 ° C. or higher, SOx is released from the NOx absorbent 62. However, in this case, the NOx absorbent 62 releases SOx little by little. Therefore, in order to release all the absorbed SOx from the NOx absorbent 62, the air-fuel ratio must be made rich for a long time, and thus there is a problem that a large amount of fuel or reducing agent is required. Further, the SOx released from the NOx absorbent 62 is discharged into the atmosphere, which is not preferable.

  Therefore, in the present invention, the SOx trapping agent 24 is disposed upstream of the NOx storing and reducing catalysts 25 and 26, and the SOx trapping agent 24 captures SOx contained in the exhaust gas. Does not flow in. Next, the SOx trap 24 will be described.

  As the SOx trapping agent 24, any SOx trapping agent may be used, but in the embodiment according to the present invention, the SOx trapping agent 24 is composed of a SOx trap catalyst. The SOx trap catalyst 24 is made of, for example, a monolith catalyst having a honeycomb structure, and has a large number of exhaust gas flow holes extending straight in the axial direction of the SOx trap catalyst 24. A catalyst carrier made of alumina, for example, is supported on the inner peripheral wall surface of each exhaust gas flow hole. FIG. 6 schematically shows a cross section of the surface portion of the catalyst carrier 80. As shown in FIG. 6, a coat layer 81 is formed on the surface of the catalyst carrier 80, and a noble metal catalyst 82 is dispersed and supported on the surface of the coat layer 81.

  In the embodiment according to the present invention, platinum is used as the noble metal catalyst 82, and the components constituting the coating layer 81 include alkali metals such as potassium K, sodium Na and cesium Cs, and alkali such as barium Ba and calcium Ca. At least one selected from earth, lanthanum La, and rare earth such as yttrium Y is used. That is, the coat layer 81 of the SOx trap catalyst 24 exhibits strong basicity.

Now, SOx contained in the exhaust gas, that is, SO ₂ is oxidized in platinum Pt 82 as shown in FIG. 6 and then trapped in the coat layer 81. That is, SO ₂ diffuses into the coat layer 81 in the form of sulfate ions SO ₄ ²⁻ to form sulfate. As described above, the coat layer 81 has a strong basicity, and therefore, a part of SO ₂ contained in the exhaust gas is directly captured in the coat layer 81 as shown in FIG.

  In FIG. 6, the shade in the coat layer 81 indicates the concentration of the trapped SOx. As can be seen from FIG. 6, the SOx concentration in the coat layer 81 is highest near the surface of the coat layer 81 and gradually decreases toward the back. When the SOx concentration in the vicinity of the surface of the coat layer 81 is increased, the basicity of the surface of the coat layer 81 is weakened, and the SOx capturing ability is weakened. Here, the ratio of the SOx trapped in the SOx trap catalyst 24 in the SOx contained in the exhaust gas is referred to as the SOx trap ratio. If the basicity of the surface of the coat layer 81 is weakened, the SOx trap ratio is accordingly increased. Will be reduced.

  The SOx trap rate is initially close to 100%, but the SOx trap rate decreases rapidly as time elapses. Therefore, in the embodiment according to the present invention, when the SOx trap rate is lower than a predetermined rate, temperature rise control is performed to raise the temperature of the SOx trap catalyst 24 under the lean air-fuel ratio of the exhaust gas, thereby The SOx trap rate is recovered.

  That is, when the temperature of the SOx trap catalyst 24 is raised with the air-fuel ratio of the exhaust gas being lean, the SOx concentrated in the vicinity of the surface in the coat layer 81 has a uniform SOx concentration in the coat layer 81. Then, it diffuses toward the back of the coat layer 81. That is, the nitrate generated in the coat layer 81 changes from an unstable state concentrated near the surface of the coat layer 81 to a stable state uniformly dispersed throughout the coat layer 81. When SOx existing in the vicinity of the surface in the coat layer 81 diffuses toward the back of the coat layer 81, the SOx concentration in the vicinity of the surface of the coat layer 81 decreases, and thus when the temperature increase control of the SOx trap catalyst 24 is completed. The SOx trap rate is restored.

  If the temperature of the SOx trap catalyst 24 is controlled to about 450 ° C. when the temperature rise control of the SOx trap catalyst 24 is performed, SOx existing in the vicinity of the surface of the coat layer 81 can be diffused into the coat layer 81, and SOx When the temperature of the trap catalyst 24 is raised to about 600 ° C., the SOx concentration in the coat layer 81 can be made fairly uniform. Therefore, during the temperature increase control of the SOx trap catalyst 24, it is preferable to raise the temperature of the SOx trap catalyst 24 to about 600 ° C. while the air-fuel ratio of the exhaust gas is lean.

  In the embodiment according to the present invention, the temperature increase control of the SOx trap catalyst 24 is performed every time the SOx trap rate decreases, and therefore the SOx trap rate can be kept high.

  However, if the amount of SOx trapped in the SOx trap catalyst 24 becomes considerably large, the SOx concentration of the entire coat layer 81 increases, and the SOx concentration in the vicinity of the surface of the coat layer 81 is sufficiently increased even if the temperature rise control of the SOx trap catalyst 24 is performed. Thus, it is difficult to recover the SOx trap rate.

  On the other hand, if the SOx releasing action that makes the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst 24 rich while maintaining the temperature of the SOx trap catalyst 24 at or above the SOx release temperature, the captured SOx is released from the SOx trap catalyst 24. Can be made. However, when the SOx trap catalyst 24 is upstream of the NOx storage reduction catalyst 25, 26 as shown in FIG. 1, if SOx is released from the SOx trap catalyst 24, this SOx is stored in the NOx storage reduction catalyst 25, 26. There is a risk.

  Therefore, in the embodiment according to the present invention, during the normal operation in which the exhaust purification module 22 is connected to the exhaust pipes 21 and 23 so that the SOx trap catalyst 24 is located upstream of the NOx storage and reduction catalysts 25 and 26, the SOx releasing action is prohibited. I am doing so. As a result, there is no possibility that SOx is stored in the NOx storage reduction catalysts 25 and 26.

  On the other hand, when the exhaust purification module 22 is connected to the exhaust pipes 21 and 23 so that the SOx trap catalyst 24 is located downstream of the NOx storage reduction catalysts 25 and 26, the SOx releasing action is allowed. That is, in the embodiment according to the present invention, it was determined whether or not the amount of SOx trapped in the SOx trap catalyst 24 exceeded the allowable upper limit, and it was determined that the amount of SOx trapped in the SOx trap catalyst 24 exceeded the allowable upper limit. In some cases, as shown in FIG. 2, the exhaust purification module 22 is inverted and connected to the exhaust pipes 21 and 23 so that the SOx trap catalyst 24 is located downstream of the NOx storage and reduction catalysts 25 and 26 so as to perform the SOx releasing action. ing.

  Whether or not the amount of SOx trapped in the SOx trap catalyst 24 exceeds the allowable upper limit is determined by, for example, an integrated value of the vehicle travel distance, an integrated value of the fuel injection amount from the fuel injection valve 3 and the fuel addition amount from the fuel addition valve 28. Can be determined based on whether or not the allowable upper limit is exceeded.

  For example, when the vehicle mileage integrated value exceeds 100,000 kilometers, it is determined that the amount of SOx trapped in the SOx trap catalyst 24 has exceeded the allowable upper limit, and the alarm device 43 (FIG. 1) is activated, so that the vehicle driver is freed of SOx. To be informed. The vehicle driver brings the vehicle to, for example, a dealer, and the exhaust purification module 22 is inverted and connected to the exhaust pipes 21 and 23 so that the SOx trap catalyst 24 is located downstream of the NOx storage reduction catalysts 25 and 26 at the dealer. Next, the SOx release switch 42 is activated, and the SOx release action is performed automatically, for example. That is, at the same time as engine operation is performed, for example, fuel is supplied from the fuel addition valve 28 so that the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst 24 becomes rich while maintaining the temperature of the SOx trap catalyst 24 at or above the SOx release temperature. Added.

  When the SOx releasing action is completed, the exhaust purification module 22 is inverted again and connected to the exhaust pipes 21 and 23 so that the SOx trap catalyst 24 is positioned upstream of the NOx storage and reduction catalysts 25 and 26.

  In this way, SOx trapped from the SOx trapping agent can be easily released while preventing SOx from being stored in the NOx storage reduction catalysts 25 and 26. In this case, since the SOx releasing action is performed by the vehicle on which the exhaust purification module 22 is mounted, no separate device is required for the SOx releasing action. Further, even if SOx is absorbed by the NOx storage reduction catalysts 25 and 26, SOx can be released by this SOx releasing action.

1 is an overall view of a compression ignition type internal combustion engine. It is a figure which shows the exhaust gas purification module reversed and connected. It is side surface sectional drawing of a 1st NOx storage reduction catalyst. It is sectional drawing of the surface part of the catalyst support | carrier of a NOx storage reduction catalyst. It is side surface sectional drawing of a 2nd NOx storage reduction catalyst. It is sectional drawing of the surface part of the catalyst support | carrier of a SOx trap catalyst.

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 Exhaust manifold 20 Exhaust after-treatment apparatus 21 Upstream exhaust pipe 22 Exhaust purification module 23 Downstream exhaust pipe 24 SOx trap catalyst 25 1st NOx storage reduction catalyst 26 2nd NOx storage reduction catalyst 28 Fuel addition valve

Claims (5)

  When the air-fuel ratio of the SOx trapping agent that temporarily captures SOx contained in the exhaust gas and the inflowing exhaust gas is lean, the NOx contained in the exhaust gas is absorbed and the air-fuel ratio of the inflowing exhaust gas becomes rich An exhaust purification module in which NOx absorbent for releasing absorbed NOx is arranged in series with each other, and the exhaust purification module is connected to the engine exhaust pipe so that the SOx trap is located upstream of the NOx absorbent; An exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas purification module is removed from the exhaust pipe and the exhaust gas purification module is inverted so that the SOx trap is located downstream of the NOx absorbent so that it can be connected again to the exhaust pipe.   SOx releasing means for releasing SOx captured from the SOx trapping agent is provided, and when the exhaust purification module is connected to the exhaust pipe so that the SOx trapping agent is located upstream of the NOx absorbent, the SOx releasing action is performed. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus is prohibited.   The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein when the exhaust gas purification module is inverted and connected to the exhaust pipe so that the SOx trapping agent is located downstream of the NOx absorbent, the SOx releasing action is allowed.   A determination means is provided for determining whether or not the amount of SOx trapped in the SOx trapping agent exceeds an allowable upper limit. When it is determined that the amount of SOx trapped in the SOx trapping agent exceeds the allowable upper limit, SOx trapping is performed. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the exhaust gas purification module is inverted and connected to the exhaust pipe so as to perform the SOx releasing action so that the chemical agent is located downstream of the NOx absorbent.   The SOx trapping agent is composed of an SOx trap catalyst, which captures SOx contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst is lean, and the air-fuel ratio of the exhaust gas is lean When the temperature of the SOx trap catalyst rises, the trapped SOx gradually diffuses into the SOx trap catalyst, and when the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst becomes rich, the SOx trap catalyst The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, which has a property of releasing captured SOx when the temperature is equal to or higher than the SOx release temperature.

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